1. Field of the Invention
The invention relates to an engine, and more particularly to a piston type pneumatic engine adopting compressed air as power source.
2. Description of the Related Art
Gasoline and diesel fuel are adopted in most of engines of automobiles as power. However, not only the exhaust of waste gas of automobiles taking the gasoline and the diesel fuel as power influences global climate, but also the development of the automobile industry is restricted by energy which becomes gradually scarce. Therefore, countries through out the world are looking for new energy which can substitute the gasoline and the diesel, as well as researching and developing the engines using new energy.
As for a common piston type engine in which the gasoline and the diesel are taken as fuel, the fuel and the air are mixed and burned in a cylinder through igniting method or compression-ignition method, and high-temperature high-pressure expanded fuel gas is produced and expanded to drive a piston to do work and to output mechanical power via a crank mechanism of a connecting rod. The cylinders of these two kinds of the engines are generally provided with an intake port and an exhaust port. The intake port is used for spraying gasoline and air which are mixed together, and the exhaust port is used for exhausting burned waste gas.
The piston type pneumatic engine is the engine taking compressed gas as power, with the advantages of cleanness, convenient air inflation and, no pollution exhaust. It has essential differences with an internal combustion engine used currently and engines taking charged batteries as power; therefore the development of the piston type pneumatic engine has become one research direction in the automobile industry. However, up to now, a series of problems of low use ratio and insufficient intensity of thrust, which are occurred when the piston of the cylinder is driven to do work by the compressed air and compressed energy of high-pressure gas is converted into mechanical energy, are not solved really.
There is a piston type pneumatic engine in the art in which compressed air is adopted as power source. The engine includes a piston cylinder. Two gas valves are arranged on a cylinder cover, wherein one gas valve is taken as an intake valve of compressed air of the power source, and the other is taken as an exhaust valve of low-pressure air after working is completed. The opening or closing time of the intake and exhaust valves is controlled by the intake and exhaust cams of the camshaft of the engine. High-pressure gas is controlled to enter, and the low-pressure gas is controlled to be exhausted. The high-pressure gas enters the cylinder through the intake valve to promote the reciprocating motion of the piston and then to facilitate the crankshaft to be rotated and generate power output. In the course of a plurality of designs and experiments, a common opening method of an internal combustion engine in which the intake valve is opened toward the inner part of the cylinder is abandoned, and an opening structure in which the intake valve is opened toward the inner part of an intake channel is adopted according to the characteristic that the compressed air has high pressure. The bigger the gas pressure in the intake channel is, the more tightly the intake port is pressed by the intake valve; therefore, the problem that the impact and leakage of high-pressure gas from the intake channel is caused by the structure that the common intake port of the internal combustion engine is opened toward the inner part of the cylinder is solved. During the experiment, it is discovered that the piston cylinder of the proposal only has working stroke and exhaust stroke. After the compressed gas enters the cylinder, the temperature in the cylinder is lowered and the use ratio of the compressed gas in the cylinder is not high. As for these problems, an improvement has been made: the suction stroke is added, and one exhaust valve is adopted to realize exhaust and suction functions at the same time. However, during the experiments, it showed that the use ratio of the compressed air was not high, which is because the intake valve is equal to a throttle valve when the high-pressure gas enters the cylinder. As the one exhaust valve not only exhausts gas but also sucks gas, the exhausted low-pressure cold compressed gas is sucked and compressed again, thus facilitating the temperature in the cylinder to become lower and lower, causing the engine to be frosted finally, causing the piston to be blocked, and lowering the use ratio of the working energy of the compressed gas.
Meanwhile, as high-pressure gas is adopted as power source, during the upward and downward long-time opening course, wear and gas leakage appear. The pressure intensity of the high-pressure gas in the intake channel and the cylinder are lowered by the gas leakage, which is the technical difficulty of the pneumatic engine. To increase sealing effect, an intake valve with better sealing effects has been developed.
With experiments, it is discovered that: being different from combustion working of the internal combustion engine, the expansion force produced when the fuel in the cylinder of the internal combustion engine is burned is relatively large, and the bore-stroke ratio of the cylinder and the piston is relatively large. However, as for the engine taking the compressed air as power source, if the bore-stroke ratio of the cylinder and the piston is too large, the resistance occurred when the piston is compressed is relatively large and power output is greatly decreased. Therefore, the proper bore-stroke ratio of the cylinder and the piston, which is researched and adopted, is also one technical difficulty of the invention.